1. Field of the Invention
The present invention relates to a system for supplying ultrapure water and a method of washing a substrate, as well as to a system for producing ultrapure water and a method for producing ultrapure water. The present invention relates, for example, to a system for supplying ultrapure water which supplies ultrapure water which is used in the washing of substrates which are to be washed, and to a substrate washing method, as well as to a system for producing ultrapure water and a method for producing ultrapure water, in washing processes for substrates which are to be washed and require highly clean washing, such as semiconductor silicon wafers, fabricated parts for precision instruments, or the like.
2. Description of Related Art
Conventionally, the following types of solutions are known as washing solutions which are used in highly clean washing.
(1) Various surfactant solutions
By means of appropriately altering the type of surfactant, it is possible to remove a wide range of substances, and at the same time, the surface tension of the solution is reduced, and thereby, it is possible to wash the interior of trenches and holes which are minute and have high aspect ratios on the surface which is to be washed.
(2) Various organic solvents
Organic solvents such as isopropyl alcohol, acetone, ethanol, and various types of freon are particularly preferable in the removal of substances which are difficult to dissolve in water, such as skin lipids and oils, and furthermore, the surface tension of these organic solvents is low, so that it is possible to wash the interior of trenches or holes which are minute and have high aspect ratios on the surface which is to be washed.
(3) Ultrapure water
Refined municipal water, well water, water for industrial use, or the like, in which the impurities present in the water have been removed to the lowest limit possible. Such water is preferable for use as a solvent, so that it is applied to the removal of various types of water-soluble substances.
However, the following problems were present in the conventional technology which employed the washing solutions listed above.
(a) When using the solution of (1) above, surfactant molecules are adsorbed to and retained on the surface which is washed, after washing.
(b) The solution of (2) above is incapable of efficiently removing water-soluble substances, and organic solvent molecules are adsorbed to and retained on the surface which is washed, after washing. Appropriate drainage and exhaust processing is necessary after such solvents are used, so that this presents problems in terms of cost. Furthermore, as a result of the danger of fire and the like, there are restrictions in the handling thereof.
(c) The ultrapure water of (3) above is incapable of washing the interior of trenches or holes having a width of 0.5 micrometers or less and having an aspect ratio or one or more.
In view of the above circumstances, the present invention has as an object thereof to provide a method for washing substrates which is capable of washing and removing trace amounts of impurities within trenches or holes which are minute and have high aspect ratios, and which is free of contamination by the washing solution, as well as a system for producing ultrapure water and a method for producing ultrapure water which are capable of obtaining ultrapure water which is used in washing.